To clarify the mode of action and physiological significance of hypothalamic hypophysiotropic hormones, particularly somatostatin. Hypothalamic hormones which have not been isolated will be purified, characterized and then synthesized. These include corticotropin-releasing factor (CRF of CRH), GH releasing factor (GRF or GHRH) and prolactin releasing factor (PRF or PRH) distinct from thyrotropin releasing hormone (TRH). Effort will be made to answer the question whether dopamine represents physiological prolactin release inhibiting factor (PIF), by examining the correlation between dopamine levels in the hypophisial portal blood and prolactin secretion.